Optimal Exhaust Size

[Revelstoke]

I searched through this forum, and I've not seen much on optimal size. I think Moose said the bigger the more expensive...good advice. My question then: will 3" be big enough? At what point am I just spending more money for very little in return?
Thanks

 

[7.3n/anut]

depends if its turbo charged or naturally aspirated. natrually aspirated the bigger the better. shoot 3'' off the turbo always worked well for me. where they connect under the cab go with whatever size you want. remember a turbo works best with a little backpressure at the turbo but not much

 

[Revelstoke]

Hey, thanks, I appreciate the input. I'm naturally aspirated, and hope to stay with that, pending some performance upgrades, I think I'll be fine. I tow a lot, so higher speeds are out anyway. So....4" would not be unwarranted?

 

[7.3n/anut]

4'' off the manifold is tight goin under the truck but doable. sounds great too.the better she breathes the better she does. by the way turnin the fuel up has negligable performance gain. just black smoke. just for show.....as i am a show off so black smke is good to me haha. jus some extra advice. if you wantram air run a scoop up behind the hood in the vents thats where fastest airflow is very helpfull in performance just an idea ive thought about

 

[Revelstoke]

YES, I have wondered, and read all I could on this forum about the "ram air" systems. I don't see where most guys agree on it, but I sure cannot help but wonder if it's better. I don't suppose it helps at low speeds, but I'm a wonderin if at about 35 (that's when I stick my fat head out the window, that the air kinda forces itself in) that the air pressurizes so to speak, and improves performance. I see production, aftermarket upgrades, and custom (cobbled together) ones, and I suppose it's just prefference at that point. More power to em' I guess.

 

[7.3n/anut]

oh absolutely. haha we did streamer tests on mine and the most streamline airflow is benind the hood right in front of the windshield. its not pretty but 4'' pvc ran back and up with a custom scoop would do the best. ima do mine as a 3'' tall by 5'' wide whenever i get to it.

 

[idi traveler]

oh absolutely. haha we did streamer tests on mine and the most streamline airflow is benind the hood right in front of the windshield. its not pretty but 4'' pvc ran back and up with a custom scoop would do the best. ima do mine as a 3'' tall by 5'' wide whenever i get to it.

PICTURES, we need pictures......please!

 

[Fozz]

According to ATS you won't get any more performance out of anything bigger than a 3 inch exhaust and that includes a turbo'd engine. That said, people have reported quicker turbo spool-up and a slight drop in EGTs with a bigger system. I just bought a 4 inch system but haven't had the time to install it yet....we'll see.

 

[The Warden]

According to ATS you won't get any more performance out of anything bigger than a 3 inch exhaust and that includes a turbo'd engine. That said, people have reported quicker turbo spool-up and a slight drop in EGTs with a bigger system. I just bought a 4 inch system but haven't had the time to install it yet....we'll see.

FWIW that's what I've heard also...anything bigger than 3" is just for show/sound. With that said, there's a guy on here with a 6.9l, Hypermax turbo, and a 5" pipe coming out just in front of the rear wheel...that truck sounds MEAN his handle's geneluo...

by the way turnin the fuel up has negligable performance gain. just black smoke. just for show

Just wondering, where did you get that from? IIRC EVERY turbo manufacturer's instructions include a part about turning up the fuel screw inside the injector pump...you'd think they wouldn't recommend that if it didn't make at least some difference...

 

[Diesel JD]

If I was N/A I would do true dual 2.5" from the manifolds back on each side and you'd probably have to put some sort of free flowing muffler in there s as not to get any noise ordinance violations unless you live way out in the sticks.

 

[Goofyexponent]

Just wondering, where did you get that from? IIRC EVERY turbo manufacturer's instructions include a part about turning up the fuel screw inside the injector pump...you'd think they wouldn't recommend that if it didn't make at least some difference...

I think he might have meant NA motors only. With the turbo (factory adn aftermarket) engines, they are getting more air so a touch more fuel is gonna help. I know all turning up those screws in my truck did was make a PILE of smoke and raise the EGT's.

 

[f-two-fiddy]

If You read the Gale Banks Memorial Library, He state's that 3" is fine for NA, 4" for Turbo Diesels. Any more did not show gains on the Dyno.

 

[icanfixall]

I have a 4 inch from the turbo down pipe back. No muffler... Thats a long piece of 4 inch pipe on a crewcab.... It plain sucks, pops, blows & goes....

 

[7.3n/anut]

Just wondering, where did you get that from? IIRC EVERY turbo manufacturer's instructions include a part about turning up the fuel screw inside the injector pump...you'd think they wouldn't recommend that if it didn't make at least some difference...

if you put a turbo on to get an effective burn and performance gain you need to get the air to ful ratio right. iff you add air youll be running lean with no power increase. they say to turn the fuel up to equal the ratio. thats why they recommend it.

 

[sootman73]

you still gotta remember that these are big motors and need big exhausts and big intakes. dual 2.5 would work but i would go with a 3.5" if single on an NA. now on a turbo motor back pressure after the turbo hurts turbo performance. you want some back pressure on N/A motors as it will hurt the scavenging process but you dont need anything after a turbo. the less back pressure the faster the turbo spools and the faster the heat can get out.

i would go with 4" on turbo'd trucks. our motors dont need anymore than that. now a psd, dirtymax, or cummins will need more because they flow tons more air than our motors.

and there is no such thing as air/fuel ratios on diesels. you can only think of it as under-fueled and over-fueled because there is no regulation of the intake air volume. plus there is no mixing of fuel and air until combustion takes place.